ran 2to3-3.3 on demjson.py and test/test_demjson.py
strip_format_control_chars was returning list after removing unicode control chars. Changed it to return string
removed check for collections.MutableString in isstringtype()
removed check for collections.MutableString in encode_string()
Fixed testEncodeObjectDictLike case. UserDict is removed from Python3. Need to use collections.MutableMapping as DictMixin instead. Also had to implement __iter__ and __len__ methods in LikeDict class